This invention relates to compressible fluid handling apparatus, and more particularly this invention relates to apparatus and method for sealing, without contact, regions of higher pressure from regions of lower pressure typically occurring in the handling of compressible fluids.
Compressible fluid handling apparatus, such as compressors or internal combustion engines, typically subject a compressible fluid, such as air, to a number of working cycles including the intake of a fluid, a subsequent compression of the fluid to a lower volume with higher pressure, and eventual discharge from the apparatus.
Typically, a movable member moving within a bounded volume, such as a cylindrical volume, will, by its movement, progressively shrink the bounded volume within which the fluid is confined to thereby move the fluid from a region of lower pressure to a region of higher pressure, i.e. compress it. Various types of compressed fluid handling apparatus include reciprocating pistons moving in a cylindrical bore, rolling pistons moving eccentrically within a cylindrical casing, and even elliptical rotors moving in epi-trochoidal paths, as in the Wankel rotary engine.
In all these instances, seals are necessary between the moving member and the bounded volume in which it moves to prevent leakage of the compressed fluid from the region of higher pressure to the region of lower pressure. Particularly in those applications, where the maximum pressure differential between the region of highest pressure and the region of lowest pressure is not excessive. The initial and most common types of seals are mechanical contact type seals (gaskets, rotative mechanical contact seals etc.). In compressed fluid handling apparatus utilizing contact type seals, wear and heat buildup are a consideration. In rolling piston designs, for example, use of the mechanical sealing elements limited the size and pressures which could be obtained by prior art configurations. In larger rolling piston compressors for example, too much heat and wear are caused by the seals to produce a long lasting configuration.
The prior art has developed so called contact-less seals which involve no contact between the moving member and its bounded volume, with the attendant benefit of significantly reduced friction.
While there exist a variety of types of prior art contact-less seals, they are essentially comprised of two different types. One type of prior art contact-less seal involves the formation of generally continuous and adjacent grooves, more or less regular, created in either, or both of, the moving member and the stationary bounded volume which are separated, not by contact but instead by a space. Such grooves create, in effect, a "labyrinth" seal with tortuous air passages which impede the flow of the compressible fluid from a region of higher pressure to a region of lower pressure. These labyrinth seals require expensive, and/or extensive, machining operations and have limited capabilities, especially when pressure differentials between regions of high pressure and low pressure become excessive driving the controlling end clearance to become exceedingly small and critical. Labyrinth seals permit fluid flow, within the seals, parallel to the grooves. This type of flow often permits an undesirable passage through the seal from regions of higher pressure to regions of lower pressures.
In an effort to overcome the cost disadvantages and limited capabilities of labyrinth-type seals, the prior art has developed an alternative seal type, known as the so-called "honeycomb" seal. Honeycomb seals are normally created by the formation of hexagonal cells formed through crimping ribbon steel and brazing together to obtain a honeycomb matrix structure which is then cut to shape and then in turn is affixed, or bonded to, either the movable element or to the stationary walls of the bounded volume within which the movable element operates.
Formation of the honeycomb cells as a separate crimped and brazed structure, and the subsequent bonding of such structure to elements of the compressible fluid handling apparatus, first requires additional manufacturing operations and further suffers from the additional disadvantage that over longer periods of service, the bond between the honeycomb structure and its associated member may weaken over time and ultimately fail. Furthermore brazing of the honeycomb structure to its associated member causes severe deformation and thermal stresses.
The foregoing illustrates limitations known to exist in present compressible fluid handling apparatus. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.